The invention relates to a burner for difficult to combust gas mixtures, particularly for exhaust gases of an internal combustion engine, wherein the burner has a combustion chamber, an ignition device and a fuel injection nozzle.
As used in connection with the present invention, the term difficult to combust gas mixtures refers to those that either contain little oxygen or include fuels that are difficult to burn, i.e. are relatively incombustible in comparison to typical fuels, such as fuel oils, kerosene and gasoline. In a principle application of such a burner, the burner is used to generate hot combustion gases that are used, for example, to initiate the regeneration of a particle filter unit in an exhaust gas duct of a diesel engine by burning off accumulated soot particles and the like in the filter unit.
In an older commonly assigned application U.S. patient application Ser. No. 235,292 filed Aug. 23, 1988), an exhaust gas burner is described, wherein an auxiliary burner for the ignition of such gas mixtures is provided which is supplied with compressed air. According to another embodiment described therein, the burner is provided with an auxiliary air injection device at the level of the fuel nozzle within the burner. These features are provided, in particular for the regeneration of an exhaust gas filter unit, so that the regeneration of the filter unit can be performed regardless of the oxygen content in the exhaust gas. In the area around the ignition device, an extremely combustible mixture is prepared so as to cause an ignition of the burner even when the oxygen content of the exhaust gas is low. As known, the oxygen content of the exhaust gas is subjected to wide fluctuations, that depend especially on the instantaneous operating level in the engine family of characteristics of diesel internal combustion engines in motor vehicles. This residual oxygen content in the exhaust gas can be between about 20% and about 4%.
In German Offenlegungsschrift No. 35 26 074, a device for removing combustible solid particles from exhaust gases of internal combustion engines is described in which a pilot burner is connected by an overflow opening to a combustion chamber, Wherein additional air and fuel are fed to the pilot burner. A partial exhaust gas stream enriched with the solid particles is introduced into the combustion chamber by a first spray nozzle tube, after which, the solid particles are burned off together with the additional air brought into the combustion chamber. Then, the stream is again carried away together with the remaining combustion products by a second spray nozzle tube as purified exhaust gas. By this device, the combustible solid particles within exhaust gas are burned in the combustion chamber directly for the purpose of exhaust gas purification. There is no description or indication of the use of this device in connection with the regeneration of soot filter units, whereas this device represents an alternative to the use of particle filter units in the exhaust gas area of a diesel engine.